Transformer oil production by acetic acid extraction



Dec. 29, 1970 3,551,324

TRANSFORMER OIL PRODUCTION BY ACETIC ACID EXTRACTION J. G. LILLARD Filed July 26, 1968 mmm.

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United States Patent O 3,551,324 TRANSFORMER OIL PRODUCTION BY ACETIC ACID EXTRACTION James G. Lillard, deceased, late of Baytown, Tex., by

Thelma C. Lillard, executrix, 3200 Garth Road, Apt.

56, Baytown, Tex. 77520 l Filed July 26, 1968, Ser. No. 749,912

Int. Cl. C10g 17/04, 21/16 U.S. Cl. 208--87 9 Claim's ABSTRACT F THE DISCLOSURE An improved transformer oil is obtained by subjecting a transformer oil base stock to extraction with concentrated acetic acid. Preferably, acetic acid containing no more than weight percent of water will be employed at `temperatures from 80 to 100 F. under conditions chosen to yield 90-95 volume percent raflinate. A solventto-oil ratio of 0.5 to 1.0 is preferred.

After-treatment may include hydrogenation and clay percolation.

The present invention relates to a novel method of producing oxidation-stable transformer oils. The present invention involves the use of an acetic acid extraction step in the sequence of treatment employed for producing transformer oils from base stocks known to be suitable for such use. As will be more fully hereinafter spelled out, the acetic acid treatment may be used at any one of several points in the treating sequence.

Transformer oils are commonly produced from highly naphthenic crude oil distillates, such as those which are obtained from Coastal crudes. One treating sequence may involve a distillation to obtain a stock of a suitable boiling range, hydroining, SO2 or phenol extraction, and percolation over Attapulgas clay. The process improvement of the` present invention, acetic acid extraction, may be used anywhere in the treating sequence upstream of the clay percolation step, and the SO2 extraction step may be omitted.

For example, the present invention may involve the acetic acid extraction of a Coastal distillate boiling within the range from 575 to 700 F. (corrected to 760 mm.) to obtain a raflinate portion amounting to from 85 to 97 weight percent of the feed to the extraction zone. The rainate is then hydrofined at a temperature from 525 to 575 F. in contact with a cobalt molybdate catalyst and at a moderate hydrogen treat rate. The hydrofined product is then contacted with Attapulgas clay in order to provide a finished transformer oil product of acceptable oxidation stability.

The present invention can best be understood by advertence to the discussions below, wherein the various maferial variables are separately treated.

Feedstock: Any suitable transformer oil base stock can be used as a feedstock in the preesnt process. -Exemplary of transformer oil feedstocks are the distillates which are obtained from Coastal crudes, such as a crude oil from the Webster Field in Harris County, Tex. The base transformer oil may comprise a single distillate, au admixture of distillates, or a distillate which has been modified by admixture with other oils such as catalytic cycle stock which has been dewaxed.

The crude distillate should boil within the range from about 550 F. to about 750 F., preferably within the range from about 575 to 700 F. Where a catalytic cycle stock is to be used (c g., from 3 to 5 volume percent of mixture), the dewaxed catalytic cycle stock should boil Within the range from 650 to 950 F., preferably from 700 to 910 F. The cycle stock is dewaxed by well-known procedures, such as MEK dewaxing.

The examples later given are based upon the use of a transformer oil base stock and a catalytic base stock distillate having the properties given below in Table I as exemplary of suitable feedstocks for use in the present invention.

TABLE I.-DISTILLATE INSPECTION DATA Catalytic Base cycle stock oil Gravity, API 28 1 18 7 Flash, COC, Viscosity at 100 F., S.S.U Viscosity at '210 F., S.S.U.. Color, Tag Robinson Refractive index at 67 C... Refractive index at 20 C. N Silica gel aromatics Boiling curves (corrected to 760 mm.) for the base stock and catalytic cycle oil are shown in the drawing.

Solvent: The solvent of the present process is a glacial acetic acid, or concentrated acetic acid having no greater than 5 Weight percent water. It has been found that concentrated acetic acid has a specicity for the removal of nitrogen compounds from transformer oils. Since hydroning has also been shown to remove basic nitrogen compounds, it is seen that the use of the acetic acid extraction in combination with hydrofining allows the user to balance the extraction efficiency with the hydrogenation conditions so that for a light extraction (e.g., about 95% raffinate yield) more severe hydrogenating conditions will be employed (for example, S50-575 F.). Conversely, where a heavy extraction has taken place (about 85% raffinate yield), the lower temperatures (e.g., S25-540 F.) will be employed. Thus, it is seen that the particular feedstock can be tested and the optimum combination of extraction rigor and hydrogenation conditions can be easily determined.

Extraction: The extraction step is carried out as is Well known in the art by one of many liquid contacting schemes; preferably a continuous, countercurrent, multiple-stage extraction will be carried out. Extraction conditions include: a temperature within the range from to 250 F. (from 80-100" F. being preferred); atmospheric or superatmospheric pressures (not critical, atmospheric pressure being preferred); a solvent-to-oil volume ratio within the range from 0.5 to 1.0 (with a ratio of 1.0 being preferred); and extraction conditions being chosen to produce a raflinate product yield within the range from volume percent to 97 volume percent of the original oil feed to the extraction zone, preferably a rafnate yield from to 95 volume percent.

The process of the present invention has been compared to various other extraction processes for treating the transformer oil base stock, such as extraction with SO2 and with sulfuric acid. Extraction with SO2 and hydrogenation are each compared below with extraction with acetic acid.

Note that all three processes reduce basic nitrogen, but acetic acid extraction does not remove 'sulfur-containing compounds, many of which are natural oxidation inhibitors.

It has also been found that the conditions under which hydrogenation is carried out can be balanced against the extraction conditions to obtain a suitable product. In summary, the results of these experiments are given below.

The finished oil (after clay treating) was subjected to a number of tests: ASTM D-l314 Sludge Test, ASTM D- 1904, Power Factor Valued Oxidation (PFVO) and the Westinghouse modification of ASTM D-943. Data from these tests are shown below, with the target values for each test.

Stability Tests:

Westinghouse (modified ASTM D-943) Inhibitor response (ASTM D1004, in-

hibited) l Laboratory reactor-Nalcomo 47l-/li9a extrudate; 1 v./v./hr. 550 p.s.i.g.; 400 s.e.. Hz/bbl.

All products clay percolated at 2 gal./

2 Pass. 3 Fail.

From the data given above, it is seen that the process of the present invention provides a novel way of obtaining a suitable transformer oil. The specificity for nitrogen compounds as opposed to sulfur compounds, exhibited by concentrated acetic acid, is nowhere duplicated in any of the other extraction agents. Thus, it is possible by using acetic acid as the extraction solvent to obtain from transformer oil base stocks a suitable and superior transformer oil product.

Finishing: The extracted base stock (rafhnate) is finished hydroning and clay treating. The hydrolining is preferably carried out in the presence of well-known hydrogenation catalysts such as nickel, platinum and cobalt molybdate. A preferred catalyst is cobalt molybdate supported on alumina and containing about 3.5 weight percent cobalt oxide and about 11.0 weight percent molybdenum oxide.

Hydrofining conditions will be correlated with the rainate yield as aforesaid, and will generally fall within the following ranges:

Temperature: 525 to 625 F. (preferably 525 to 575 lPressure: 500 to `600 p.s.i.g. (preferably 550 p.s.i.g.)

Space velocity: 0.5 to 5 v./v./hr. (preferably 1.0 v./v./hr.)

Hydrogen rate: 200 to 500 s.c.f./bbl. (preferably 400 The hydroined product is clay contacted (preferably by percolation), with adsorptive clays such as Attapulgas clay. A treat rate of about 2 gallons of oil per pound of clay has been found to be suitable, although from 1 to 5 gallons per pound should also be suitable.

In order to more fully disclose the basis of the present invention, the following examples are given.

EXAMPLES Example 1 A transformer oil base stock as shown in Table I Iwas extracted with glacial acetic acid. The extraction was 3- stage, countercurrent. Extraction conditions included a temperature of 75 F., atmospheric pressure and a solvent-to-oil ratio of 0.5 to obtain a rainate yield of 97%. The raffinate was stripped under a nitrogen blanket and then hydroned in contact with a Nalco 471 cobalt molybdate catalyst at a temperature of 540 F., a pressure of 560 p.s.i.g., a space velocity of 1.5 v./V./hr., and a hydrogen treat rate of 400 s.c.f. per barrel of oil charged. After the hydrogen treating, the oil was percolated over Attapulgas clay at a treat rate of 2 gallons 0f oil per pound of clay.

Stability test Target Test result Evaluation D-ieo4 722 Pass. D-1314 1 0.075/0.l5/0.30 3 0.06/0.14/0.24 Pass. IFVO 50 2 50 4 Marginal. Westinghouse. 2 100+ Pass.

lValues for sludge at three days/seven days/fourteen days. Expressed as percent by weight based 0n the sample oil.

2 Hours minimum.

3 Maximum.

4 Hours.

It is thought that raising the hydrofining temperature to 550 F. would have produced a suitable product.

Example 2 A transformer oil base stock as shown in Table I was admixed with a dewaxed catalytic cycle stock distillate as also shown in Table I. The catalytic cycle stock comprised 5 volume percent of the mixture. The mixture was extracted with glacial acetic acid as in Example l, but through four stages; then the raffinate was stripped under a nitrogen blanket to a still temperature of 320 F. Raflinate yield was 95.8 volume percent.

The stripped raflinate was hydrofined in contact with cobalt molybdate catalyst at a temperature of 525 F., a pressure of 550 p.s.i.g., a space velocity of 1.0 v./v./ hr., and a hydrogen treat rate of 400 s.c.f./bbl. The hydrofined oil was percolated over Attaplugas clay at the treat rate of 2 gallons per pound of clay.

The finished oil was subjected to a number of tests.

Results are shown below.

Stability Test Target Test Result Evaluation D-1904, life hours 72 2 64 3 Fail. D-1314, sludge at 3 days/ 7 days/14 days-.. 0.075/0.15/0.30 0.04/0.09/0.13 Pass. PFVO 60 2 90 a Pass. Westinghouse life.. 100 2 1, 000 Pass. Inhibitor response l. 600 2 360+ Fail.

l D-1904, but oil is first inhibited with 0.15 Weight percent of 1,3fdi-tert butyl-2-hydroxy-S-mcthylbenzene, an oxidation inhibitor.

2 Hours minimum.

SHours.

The failure to meet the D-1904 and inhibitor response tests was thought to be attributable to the combination of low extraction (95.8 weight percent raffinate) and mild hydroning (525 F.), and that a higher hydrofning temperature would have produced an acceptable product.

Example 3 A mixture of 97 volume percent transformer oil base with 3% cycle stock, each as shown in Table I. was sub- Result, Evalua- Test Target hours. tion.

D1904 life 1 72 72 Pass. D-1314, sludge at 3 days/7 days/14 days 0.075/0.15/0.30 0.06/0.09/0.17 Do. PFVO 150 90 Do. Westinghouse 1 100 192 Do. Inhibitor response 1 600 672 Do.

1 Hours minimum.

From Example 3 it is seen that an increase in the extraction severity (lowering raiinate yield from 95.8% to 84.4 volume percent) counteracted the low (525 F.) hydroning temperature. The product passed all tests.

Example 4 A transformer oil base stock as shown in Table I was subjected to 6-stage countercurrent extraction with glacial acetic acid at 75 F., atmospheric pressure, and a solventto-oil ratio of 1.0, to a raiinate yield of 83.1%. The raffinate was split and hydroned in contact with a cobalt molybdate catalyst at 525 F., 550 F., and 575 F., at a pressure of 550 p.s.i.g., a space velocity of 1.0 v./v./hr., and a hydrogen treat rate of 400 s.c.f./bbl. The catalyst in each case was Nalco 471. Hydroned raffinate was clay treated to 2.0 gallons per pound. Results of testing are shown below.

4. In the production of a transformer oil from a transformer oil base stock boiling within the range from 550 F. to 750 F.,

the improvement of extracting said base stock with concentrated acetic acid containing not more than 5 weight percent of water under conditions including:

a temperature from 75 F. to 250 F., a solvent/oil volume ratio from 0.5 vto 1.0, and a Contact time chosen to produce a raflinate yield from 85 volume percent to 95 volume percent, base on oil feed, thereafter hydrogenating said rainate in contact with a hydrogenation catalyst at a temperature from 525 F. to 625 F., a pressure from 500 p.s.i.g. to 600 p.s.i.g., a space velocity from 0.5 to 5 v./v./hr., and a hydrogen rate from 200 to 500 sci/bbl.,

wherein the catalyst comprises 3.5 Weight percent cohalt oxide and 11.0 weight percent molybdenum oxide on alumina, and

wherein the feedstock to the extraction step contains from 0 t0 5 volume percent of a catalytic cycle stock and from 97 to 95 volume percent Coastal distillate, said distillate and said catalytic cycle stock having Result Stability Test Target 525 F., hours 550 F., hours 575 F., hours D-1904, life 1 72 72 40 64 D-1314, sludge at 3 days/7 days/14 days 2 0.075/0.15/0.30 0. 08/0. 16/0. 26 0.06/0. Bti/0.71 0. 03/0.46/1. 03

FVO life 1 50 90 90 90 Westinghouse 1 100 108 48 48 Inhibitor response 1 600 672 3 504: 720

l Hours, minimum. 2 Maximum. 3 Data questionable, may have passed.

From the data above, it is seen that the higher hydrolining temperature (550 F. and 575 F.) are unsuitable for heavily extracted oils (82.1% raflinate yield), but that the lower temperature (525 F.) in combination with heavy extraction produces a suitable product.

I claim:

1. In the production of a transformer oil from a transformer oil base stock boiling within the range from 550 F. to 750 F.,

the improvement of extracting said base stock with concentrated acetic acid containing not more than 5 weight percent of water under conditions including:

a temperature from 75 F. to 250 F.,

a solvent/oil volume ratio from 0.5 to 1.0, and

a contact time chosen to produce a rainate yield from 85 volume percent to 95 Volume percent, based on oil feed,

and thereafter hydrogenating said ratiinate inl contact with a hydrogenation catalyst at a temperature from 525 F. to 625 F., a pressure from 500 p.s.i.g. to 600 p.s.i.g., a space velocity from 0.5 to 5 v./v./hr., and a hydrogen treat rate from 200 to 500 s.c.f./bbl.

2. A method in accordance with claim 1 wherein the acetic acid is glacial acetic acid, the temperature is from 80 F. to 100 F., the solvent/oil ratio is 1.0, and the raffinate yield is from 90 to 95 volume percent.

3. A method in accordance with claim 2 wherein the catalyst comprises 3.5 weight percent cobalt oxide and 11.0 weight percent molybdenum oxide on alumina.

5. A method in accordance with claim 4 wherein the extraction solvent is glacial acetic acid and the extraction temperature is from F. to 100 F., and the raliinate yield is from volume percent to 95 volume percent.

6. A method in accordance with claim 5 wherein the hydrogenation temperature is from 525 F. to 550 F.

7. A method in accordance with claim 3 further comprising the step of percolating the hydrotreated oil over Attapulgas clay.

v8. A method in accordance with claim 6 further comprising the step of percolating the hydrotreated oil over Attapulgas clay.

9. A method in accordance with claim 8 wherein the percolation treat rate is about 2 gallons of oil per pound of clay.

References Cited UNITED STATES PATENTS 2,100,707 11/ 1937 Bhatnagar 208-328 2,288,373 6/ 1942 Smith et al. 208-14 2,984,617 5/ 1961 DeChellis et al 208--90 3,252,887 5/ 1966 Rizzuti 208-14 3,406,111 10/ 1968 Wynkoop et al 208--14 HERBERT LEVINE, Primary Examiner U.S. C1. X.R. 

